1. Field of the Invention
This invention relates to a touch-operable power control system.
2. Description of the Related Art
Dimming or lighting loads is desirable to conserve energy, increase lamp life, and aesthetically improve the human environment. Well known circuit methods, such as phase control, are widely used to vary the power delivered from an AC source to a lighting load.
Some dimming circuits, such as that disclosed in U.S. Pat. No. 3,746,923, issued Jul. 17, 1973, to Spira et al. (Spira et al.), incorporated herein by reference, are adapted to fit in a standard electrical wallbox of the type used to house conventional toggle light switches. Other circuits, generally for controlling larger amounts of power, require cabinets that can be installed in an electrical closet or basement. In either case, a dimmer actuator is manipulated to adjust the brightness of the lighting load. Some dimming circuits are controllable by a number of remotely located actuators, each actuator operable to "take command" (of the dimming circuit) from the other actuators. (See, for example, U.S. Pat. No. 4,689,547, issued Aug. 25, 1987, to Rowen et al.)
Many types of actuators are used to operate dimming circuits. The earliest actuators were rotary. Rotary actuators generally include a round knob that can be rotated about a central axis. A rotary potentiometer mounted behind the knob is operated thereby to provide a signal, such as variable voltage or resistance, to control the power provided by the dimming circuit to the load. One drawback of rotary actuators is that one cannot easily tell the light level (of a lighting load in an adjacent room, for example) from the orientation of the knob. A cover plate generally fits between the knob and the potentiometer to protect the potentiometer from dust and dirt to provide an aesthetically pleasing appearance. As used in this specification and the appended claims, a cover plate is understood to have a front and back surface. The front surface is generally prominent and aesthetically pleasing. The back surface is generally hidden from view.
Linear slide actuators of the type disclosed in Spira et al. have gained widespread acceptance in the dimming industry. They generally include a slider that moves linearly along a predetermined path. A linear potentiometer mounted behind the slider is operated thereby to provide a variable voltage or resistance to the dimming circuit. Generally, linear slide dimmers permit lighting levels to be determined easily from the slider position.
A more recent development has been the "Touch-actuated dimmer." A touch dimmer generally includes a touch- or pressure-operated device which controls a conventional dimming circuit. Since these devices are typically small and thin, they permit touch dimmers to be flat, compact, and less conspicuous than mechanically operated dimmers. The rugged construction of touch-operated devices makes these dimmers durable and reliable.
One type of touch dimmer, manufactured by Home Automation, has a conductive cover plate which is electrically connected to a control circuit. Touching a finger or the like to the conductive plate increases its electrical capacitance, which is detected by the control circuit. The control circuit provides signals to a dimming circuit for controlling power to a load. The system operates as follows: When a finger is held in contact with the plate, the brightness of a lighting load cycles through a range of selectable light levels. Removing the finger stops the cycle at a particular light level, which is maintained thereafter. Momentarily touching the conductive plate alternately turns the lighting load off and on to the most recently set lighting level. A drawback of this type of touch dimmer is that adjusting the lights requires cycling through a range of light levels before arriving at the desired level. Furthermore, since there is a delay in the eye's response to changing light levels, it may be difficult to stop the cycle at a light level that will be appropriate once the eye has adjusted.
The Touch-A-Level.RTM. lamp dimmer, manufactured by Westek, San Diego, Calif., can be plugged into a wall outlet to control up to 200 W of power from an electrical outlet to a table-top lamp. It is touch-operated to instantly select, from a range of levels, the power delivered to the lamp. The dimmer includes an elongated flexible strip of plastic, containing a number of electrical contacts along its length, adhered to the front surface of a plastic cover plate. Touching the flexible strip at any point along its length causes one or more contacts to close, providing a signal that corresponds to a particular light level. The contacts are arranged to provide a discreet range of approximately 25 selectable light levels. Two drawbacks of the Westek dimmer are that it does not provide a continuous range of selectable light levels and that the flexible strip adhered to the cover plate may peel off with extended use.